A police officer wearing a bulletproof vest stands guard at the main train station in Berlin, Germany, Nov. 17. Germany is increasing security throughout the country, particularly in airports and train stations.

Germany is increasing security throughout the country, particularly in airports and train stations, on the basis of "concrete indications of a series of attacks planned for the end of November," Interior Minister Thomas de Maizière said today.

Dr. Maizière told citizens to be ready for a "visible police presence," which Agence France-Presse reported was already apparent today as "machine gun-toting police patrolled German stations and airports ... there could also be tighter checks on the external borders of the European Schengen visa-free travel zone."

The tip-off about the potential attack came from a "foreign partner" and comes two weeks after Saudi Arabia helped Western authorities foil a bombing attempt by Al Qaeda in the Arabian Peninsula (AQAP). The Yemen-based group concealed bombs inside computer-printer ink cartridges destined for Chicago synagogues and shipped in FedEx and UPS planes. The bombs were discovered in Britain and Dubai on Oct. 29. One of the planes passed through Germany's international airport on Cologne with the lethal cargo undetected.

"Our measures are intended to prevent and deter terrorist attacks. We will demonstrate strength and will not be intimidated. The public will be able to see these police measures, but there will also be many measures you will not be able to see," Maizière said in a statement today in Berlin.

Maizière said the Interior Ministry had "further relevant information" regarding potential Al Qaeda attacks on the United States and Europe, including Germany. "We have cause for concern, but no reason for hysteria. We will not allow international terrorism to interfere with our daily lives nor with our democratic way of life," he added.

In addition to intelligence from the unnamed nation, Germany's Federal Criminal Police Office independently confirmed, based on investigations "of persons with ties to Islamist extremism... that Islamist groups continue to plan attacks in the Federal Republic of Germany."

According to Germany's Tagesspiegel daily, the United States is the "foreign partner" who provided the tip-off. Up to four Al Qaeda operatives were on their way to Germany to attack the popular Christmas shopping markets, according to Tagesspiegel, and expected to arrive Nov. 22 via India or the United Arab Emirates.

Germany's Interior Ministry responded with a degree of skepticism in late September when reports emerged of an Al Qaeda plot to carry out coordinated Mumbai-style terrorist attacks in major cities in Britain, France, Germany, and possibly the United States.

The US and Japanissued Europe-wide travel alerts and Britain raised its terror warning to "high" for its nationals in France and Germany. But, at the time, Maizière said in a statement that "there are currently no concrete indications of imminent attacks in Germany."

Despite the increased police presence and heightened security, Chancellor Angela Merkel's chief spokesman, Steffen Seibert, told the Wall Street Journal the German leader would not be changing her travel plans. "We'd be making a big mistake as a society if we let this totally change what we do," Mr. Seibert said.